Separate exciter windings for weld and auxiliary power

ABSTRACT

A method and apparatus for providing power from an engine includes a one or more output windings in of slots on a generator. A plurality of exciter windings are in magnetic communication with the one or more output windings. The exciter windings are also placed in slots in the generator. The location of slots for the various windings is chosen to produce a desired output. A power supply is in electrical communication with the one or more output windings. Preferably, there are as many or more exciter windings as there are output windings.

FIELD OF THE INVENTION

[0001] The present invention relates generally to the art of enginedriven welding power supply systems. More specifically, it relates toengine-driven welding power supply systems with a welding power outputand an auxiliary power output.

BACKGROUND OF THE INVENTION

[0002] Engine driven welding power supply systems may be driven eitherby a DC generator or an AC generator (also called analternator-rectifier). An AC generator generally includes, in additionto an alternator, a reactor followed by rectifiers to provide a DCoutput. One prior art engine-driven welding power supply system is theMiller Bobcat 225® welding power supply. (Engine-driven welding powersupply system, as used herein, includes one or more of the engine, thegenerator, and the power supply. Welding power supply, as used herein,includes power supplies that provide welding, plasma or heating power,and may include a controller, switches, etc.).

[0003] The Miller Bobcat 225® welding power supply includes a generatorhaving a single primary mover, with a single exciter, stator and rotorto provide a welding power output and an auxiliary power output. Theauxiliary power is 60 Hz power, 120/240 volts used to operate lights,tools, and other 60 Hz. loads. The auxiliary power is ideally asinusoidal, constant voltage source (like utility power).

[0004] The welding output is derived from a single phase welding outputwinding, and the auxiliary power is derived from a single phaseauxiliary output winding that are part of the generator stator. (Outputwinding, as used herein, includes a winding connected to be able toprovide power to a load.) These windings are electrically isolated fromeach other, but are in magnetic communication (magnetic communication,as used herein, includes windings wherein a single revolving magneticfield is provided to both windings, and/or the windings are wound abouta common stator). The magnetic field is created by passing a dc fieldcurrent through the winding on the rotor. The dc field current isderived from a single excitation winding in the generator stator—thewelding power and the auxiliary power share an excitation winding.(Excitation or exciter winding, as used herein, includes a windingconnected to provide current to a field winding).

[0005] When there is a current output the load current flows in thestator windings and creates a magnetic field called the armaturereaction field. The armature reaction field increases with load current.The combination of the magnetic field from the field winding and thearmature reaction field is the net magnetic field that produces weldingand auxiliary output power.

[0006] The armature reaction field opposes the field produced by thefield windings on the rotor and reduces the net magnetic field in thegenerator, which reduces the output voltage of the generator. Thereduction in net magnetic field and output voltage increases as the loadcurrent increases, because the armature reaction field increases withload current. Such a voltage reduction is particularly undesirable forauxiliary power, which is ideally a constant voltage source (to mimicutility power).

[0007] Prior art engine driven welding power supply systems attempt tocompensate for the armature reaction field by increasing the fieldcurrent. However, the resistance of the field winding (rotor coil)requires that, to increase field current, the voltage applied to thefield windings must be increased. The field current is increased byincreasing the voltage supplied to the field windings. The increasedfield voltage is provided by increasing the voltage supplied by theexcitation winding on the stator.

[0008] One prior art technique to increase the field current isdescribed in U.S. Pat. No. 5,734,147, issued Mar. 31, 1998, entitledMethod And Apparatus For Electronically Controlling The Output Of AGenerator Driven Welding Power Supply, Bunker et al., incorporatedherein by reference. Electronic control and feedback is used to adjustthe field current to the desired magnitude. This is an effective way tocontrol the field current, but it requires a relatively sophisticatedand costly electronic control scheme.

[0009] Another prior art engine driven welding power supply systems, theMiller Bobcat 225®, uses a simple system with no electronics or printedcircuit boards. The excitation winding in the stator is connected to adiode bridge to rectify the current to dc, a capacitor for smoothing,and a variable resistor, for controlling the magnitude of the fieldcurrent. A variable resistor may be included to compensate fortemperature drift. Generally, the system provides for an increasedexciter voltage (which increases field current) by using the influenceof the load current flowing in other windings on the stator.Specifically, single phase load currents cause a harmonic interaction inother windings in the stator.

[0010] Prior to explaining how these components compensate for thearmature reaction field, a brief discussion of the harmonic interactionis useful. A single phase load current flowing in a stator windingcauses a pulsating magnetic field. The pulsating magnetic field can beresolved into two components, one that rotates in the forward direction,with the rotor, and one that rotates in the opposite direction. Statedanother way, when the load is unbalanced the magnetic field wave createdby the stator currents does not move at the speed as the rotor and maybe resolved into two components: a forward component that is in the samedirection and at the same speed as the rotor, and a backward component.The forward component behaves as a balanced three phase load. Thebackward component moves at the same speed as the rotor, but in theopposite direction. Thus, it has a motion relative to the rotor of twicethe generator speed. This “moving” magnetic field induces voltage in theexcitation winding, which causes a higher output voltage. This phenomenais described in Engine Driven Invertor With Feedback Control, Beeson etal, issued Oct. 19, 1999 as U.S. Pat. No. 5,968,385, which isincorporated herein by reference.

[0011] The “backward” component of the magnetic field induces ac currentat twice the fundamental frequency in the rotor winding (because therelative speed of the backward component is twice the rotor speed). Thesecond harmonic component of field current in the rotor causes harmonicvoltages to be induced in the stator windings. The primary harmonic inthe stator windings is the third harmonic (the second harmonic of thefield current plus the speed of the rotor).

[0012] The relative phasing of the third harmonic and the fundamentalinfluence the shape of the resulting voltage waveform, such as beingflat-topped, or reduced shoulders with an increased peak voltage. A highpeak voltage provides maximum boosting under load. The Miller Bobcat225® engine driven welding power supply system captures the high peakvoltage with the capacitor connected to the excitation windings, smoothsthe voltage and applies it to the field winding, which in turn drivesmore field current, and boosts the output.

[0013] The desired relative phasing between the fundamental and theharmonics is effected by the placement of the excitation windings andthe output windings—i.e. in which slots the windings are placed. Becausethere are separate welding output and auxiliary output windings, therelative placement of the excitation and load windings, and the relativephasing of the harmonics, will be different for the welding output andthe load output. Thus, the placement of the single exciter winding mustbe based on desirable welding output, a desirable, auxiliary output, ora compromise therebetween.

[0014] The Miller Bobcat 225® engine driven welding power supply systemhas the exciter winding placed to provide a greater output boost for thewelding output windings (to provide a desirable welding output).Unfortunately, providing the additional power for welding results inlittle output boost for an auxiliary load.

[0015] This provides a desirable welding output, but at the expense ofauxiliary power. Specifically, the generator folds back as the auxiliaryoutput is loaded, which results in low auxiliary power output inproportion to the size of the generator. The problem is exacerbated whenthe system is used to start an electric motor.

[0016] Accordingly, an engine-driven welding power supply system thatprovides an output boost for both welding output and auxiliary output isdesirable. Preferably, such a system will be relatively simple and notcomplex or costly.

SUMMARY OF THE PRESENT INVENTION

[0017] According to a first aspect of the invention an engine-drivenwelding power supply system includes welding and auxiliary outputwindings, and a welding and auxiliary exciter windings in magneticcommunication with the output windings. A welding power supply isconnected to output windings, and the power supply provides a weldingoutput and an auxiliary output.

[0018] The welding output winding and the auxiliary output winding arein magnetic communication in one embodiment, and are wound about acommon stator in another embodiment. The welding exciter winding and theauxiliary exciter winding are wound about the common stator in yetanother embodiment.

[0019] A field winding receive field current from the welding exciterwinding and from the auxiliary exciter winding in another alternativeembodiment. A rectifier is disposed between the welding exciter windingand the field winding, and another rectifier is disposed between theauxiliary exciter winding and the field winding in other embodiments. Acontroller is connected to the welding power supply and the fieldwinding in yet another embodiment. The generator is preferably an acgenerator.

[0020] The placement of the various windings, the auxiliary output issuch that the welding output and the auxiliary output are optimized inan alternative embodiment.

[0021] A second aspect of the invention is a method of providing weldingand auxiliary power that includes turning a primary mover, inducingcurrent in a welding output winding, inducing current in a weldingexciter winding in magnetic communication with the welding outputwinding, inducing current in an auxiliary output winding, and inducingcurrent in an auxiliary exciter winding in magnetic communication withthe auxiliary output winding. The output of the welding output windingis provided to a welding power output and the output of the auxiliaryoutput winding is provided an auxiliary output.

[0022] Inducing a current in the welding output or exciter windingsinduces a current in the auxiliary output or exciter winding in variousalternatives. The welding output windings and the auxiliary outputwindings are wound about a common stator associated with a rotor, andturning the primary mover turn the rotor in another embodiment.

[0023] The location of the welding output winding, the auxiliary outputwinding, the welding exciter winding and the auxiliary exciter windingare determined by determining the placement that optimizes the weldingoutput and the auxiliary output in another embodiment.

[0024] Current from the welding exciter winding and from the auxiliaryexciter winding are rectified and/or provided to a field winding invarious embodiments.

[0025] AC power is generated in another embodiment.

[0026] Another aspect of the invention is engine-driven power supplysystem includes an output winding, a first exciter winding, and a secondexciter winding, in magnetic communication with one another. A powersupply is connected to the output winding. An alternative includes asecond output winding.

[0027] Another aspect of the invention is an engine-driven welding powersupply system having a generator, including a stator with a plurality ofslots. A welding output winding is wound in a first subset of theplurality of slots to provide a magnetic axis in a first direction. Awelding exciter is wound in a second subset of the plurality of slots toprovide a magnetic axis in a second direction. An auxiliary outputwinding is wound in a third subset of the plurality of slots to providea magnetic axis in a third direction. An auxiliary exciter winding iswound in a fourth subset of the plurality of slots to provide a magneticaxis is in a fourth direction. A welding power supply is in electricalcommunication with the welding output winding and the auxiliary outputwinding. The welding power supply has a welding output and an auxiliaryoutput.

[0028] The angle between the first direction and the second direction issuch that a desired welding output is produced, and/or the angle betweenthe third direction and the fourth direction is such that a desiredauxiliary output is produced in various alternatives.

[0029] The angle between the first direction and the second direction issuch that a welding exciter winding voltage increases as the weldingoutput winding is loaded, and/or the angle between the third directionand the fourth direction is such that an auxiliary exciter windingvoltage increases as the auxiliary output winding is loaded in otheralternatives.

[0030] The angle between the third direction and the fourth direction isempirically determined and/or calculated in alternative embodiments.

[0031] Another aspect of the invention is a method of designing anengine-driven welding power supply system. The system has a generatorwith a stator with a plurality of slots, a welding output winding, awelding exciter winding, an auxiliary output winding, and an auxiliaryexciter winding. The method includes winding the various windings in avarious subsets of the slots such that each winding has a magnetic axis.The magnetic axis of the welding output winding is in a first direction,the welding exciter winding magnetic axis is in a second direction, theauxiliary output winding magnetic axis is in a third direction, andauxiliary exciter winding magnetic axis in a fourth direction. A weldingpower supply is connected to the welding output winding and theauxiliary output winding, and the welding power supply provides awelding output and an auxiliary output.

[0032] The angle between the auxiliary output and exciter windingmagnetic axes is empirically determined and/or calculated in variousalternatives.

[0033] Yet another aspect of the invention is an engine-driven powersupply system including a plurality of output windings in a firstplurality of slots and a plurality of exciter windings in a secondplurality of slots. The exciter windings are in magnetic communicationwith the output windings. The location of the first and second pluralityof slots is such that a desired output is produced. A power supply isconnected to the output windings.

[0034] According to one alternative, there are as many or more exciterwindings as there are output windings.

[0035] Other principal features and advantages of the invention willbecome apparent to those skilled in the art upon review of the followingdrawings, the detailed description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036]FIG. 1 is a block diagram of a welding system constructed inaccordance with the preferred embodiment;

[0037]FIG. 2 is schematic diagram of a generator constructed inaccordance with the present invention;

[0038]FIG. 3 is a schematic showing the slot location of a weldingoutput winding in accordance with the preferred embodiment;

[0039]FIG. 4 is a schematic showing the slot location of a weldingexciter winding in accordance with the preferred embodiment;

[0040]FIG. 5 is a schematic showing the slot location of an auxiliaryexciter winding in accordance with the preferred embodiment;

[0041]FIG. 6 is a schematic showing the slot location of an auxiliaryexcitation winding in accordance with the preferred embodiment; and

[0042] FIGS. 7-9 are phasor diagrams related to the preferredembodiment.

[0043] Before explaining at least one embodiment of the invention indetail it is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangement of thecomponents set forth in the following description or illustrated in thedrawings. The invention is capable of other embodiments or of beingpracticed or carried out in various ways. Also, it is to be understoodthat the phraseology and terminology employed herein is for the purposeof description and should not be regarded as limiting. Like referencenumerals are used to indicate like components.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] While the present invention will be illustrated with reference toa particular engine-driven welding power supply system and particularcomponents, electronics, Nwindings etc., it should be understood at theoutset that the invention may also be implemented with other systems andcomponents, that provide welding and auxiliary power, or that provideother types of power. Generally, the invention is most applicable whenat least two types of output power is provided.

[0045] A welding system 100 in accordance with the preferred embodimentincluding an engine or primary mover 101, a generator 103 and a weldingpower supply 105, is show in FIG. 1. Welding system 100 provides awelding output 106 and an auxiliary output 107. The preferred embodimentis generally implemented using a welding system such as the MillerBobcat 225®. The engine, generator and welding power supply can be partof a single package, or can be in discreet modules or cases.Additionally, welding power supply 105 includes a controller which canbe in a discreet module or case.

[0046] Generally, engine 100 rotates a rotor in generator 103. Generator103 is in electrical communication with welding power supply 105, or hasan electrical output provided as an input to welding power supply 105.(Electrical communication with, as used herein, includes a connectionwherein electrical signals and/or power may be provided or received.)Welding power supply 105 provides welding output 106, which is typicallylow voltage and high current (20-40V and 100-225 amps), and auxiliaryoutput 107 which is 60 Hz, 120/240V, with sufficient current to powerhand tools, lights etc.

[0047] Unlike prior art systems generator 103 includes two exciterwindings on the stator. The placement (or slot location) of exciterwindings relative to load windings in a single-phase generator canaffect the field current that is supplied to the field. One exciterwinding is placed such that the phase between the fundamental andharmonics result in an exciter voltage shape having reduced shoulderswith an increased peak voltage when there is a welding output. The highpeak voltage is captured by a capacitor and provides maximum boostingunder load, which is a desirable welding output. The other exciterwinding is placed such that the phase between the fundamental andharmonics result in an exciter voltage shape having reduced shoulderswith an increased peak voltage for the auxiliary output. The high peakvoltage is captured by the capacitor and provides maximum boosting forthe auxiliary output, which is a desirable auxiliary output. The twoexciter winding outputs are combined with diodes, so that the greaterexciter output is provided to the field winding. Generally, the exciterwindings voltages increase as the output windings are loaded. This inturn will drive more field current, which maintains the output voltageconstant. More specifically, as shown in FIG. 3 generator 103 includes awelding output winding 201, an auxiliary output winding 203, a weldingexcitation winding 205, an auxiliary excitation winding 207, rectifiers208 and 209, and a capacitor 210. The output of welding winding 201 isprovided to welding power supply 105 (FIG. 1). The output of auxiliarywinding 203 is also provided to welding power 105, which provides it asthe AC auxiliary output. The auxiliary and welding outputs arepreferably electrically isolated from one another. The AC auxiliaryoutput is located directly on the generator in some embodiments. Weldingexcitation winding 205 provides current through rectifier 208 to thefield winding. As stated above, welding excitation winding 205 is placedon the stator to provide a desirable boost to the field current whenthere is a welding output (which causes a desirable boost in the weldingoutput). Windings 201, 203, 205 and rectifier 208 are similar to theprior art.

[0048] Auxiliary winding 207 provides its output through rectifier 209to the field winding. Because the excitation winding outputs areprovided through rectifiers 208 and 209, their outputs are effectively“ORED”—the greater voltage from the two excitation windings is appliedto the field winding. Rectifiers 208 and 209 are full bridge rectifiersin the preferred embodiment, but may be half-bridges or combinedrectifiers in alternative embodiments. Capacitor 210 smooths the outputsof rectifiers 208 and 209 and captures the high peak voltages. Capacitor210 should have sufficient capacitance to provide the amount ofsmoothing desired. As stated above, auxiliary excitation winding 207 isplaced on the stator to provide a desirable boost to the field currentwhen there is an auxiliary output (which causes a desirable boost in theauxiliary output).

[0049] One alternative embodiment includes a single output winding andtwo excitation windings. This embodiment may be useful when the singleoutput winding is used for two or more applications having differentdesired V-A curves, or a single application with a V-A curve withmultiple breakpoints. Another embodiment includes more output windingsthan excitation windings. Yet another embodiment includes moreexcitation windings than output windings. Generally, the inventionincludes multiple excitation windings, where each excitation windingprovides an output boost at a desired phase and/or desired output range.An exciter winding voltage increases as the output windings are loadedto drive more field current, thus maintaining a constant output voltage.Alternatively, the exciter windings could be placed to provide adrooping or other characteristic output. Generally, the slot locationare chosen to optimize the output. (Optimize the output, as used herein,refers to obtaining an output having desired charateristics, givendesign constraints such as cost, weight etc.).

[0050] The slot location of the various windings will determine theshape of the output curve. Specifically, the slot location determinesthe relative phase of the fundamental and the third harmonic, whichdetermines the relationship of the boost to the unboosted output. Theslot location is thus chosen, in the preferred embodiment, to provide adesired output shape. The preferred slot location is determinedempirically, by calculation, and a combination thereof in variousembodiments.

[0051] The calculation is based on the power factor of the load, numberof turns of the output winding, number of turns of the field winding,and resistance of the field. The welding output circuit has a reactorwith different taps for different output current ranges. The taps causethe power factor of the load to be different for different ranges. Thedifferent power factor for the different ranges means that each rangeposition theoretically has a different exciter placement. The placementfor a single exciter that provided the best boosting effect over all theweld ranges was empirically determined. Alternatively, exciters fordifferent ranges could be provided.

[0052] FIGS. 3-6 show slot locations for the welding output, weldingexcitation, auxiliary output, and auxiliary excitation windings,respectively. The magnetic axis is shown as 302, 402, 502 and 602,respectively. These slot locations for the preferred embodiment, arewell suited for a Miller Bobcat®-type machine (with the added excitationwinding). The slots chosen for the welding output are 33-5 and 23-15,which provide the magnetic axis 302 at slots 10-28 (referenced as 0degrees). The slots for the welding excitation winding, determinedempirically and by calculation, are 29-31 and 15-13, which provide amagnetic axis from slot 22-4 (60 degrees). The slots for the auxiliaryoutput winding, were chosen to be slots 23-32 and 14-6, which provide amagnetic axis from slot 19-1 (90 degrees). The slots for the auxiliaryexcitation winding, determined empirically and by calculation, are 22-24and 86, which provide a magnetic axis-from slot 15-33 (130 degrees).Thus, the phase difference of the welding output and excitation windingsis 60 degrees, while the phase difference of the auxiliary output andexcitation windings is 40 degrees. These relative phases produce adesired boost for the welding output, and a desired boost for theauxiliary output.

[0053] The empirical determination of the desired slot may be made byplacing windings in various slots, and monitoring the output.Alternatively, the following model and calculations may be used todetermine the correct placement of exciter windings in a single phaseself excited -generator.

[0054] The single-phase generator of the preferred embodiment is used asthe model. A brief review of that generator is useful before beginningthe calculations. It has two single phase output windings in the samestator; one winding is for welding output, the other for auxiliaryoutput. The field excitation is derived from the exciter windingsthrough diode bridges, rheostat, and brushes to the rotating field. Thevoltage output from the exciter windings are influenced by the load inthe weld or auxiliary output windings. The ideal is to have the exciterwinding voltage increase as the output windings are loaded. This drivesmore field current to maintain the output voltage constant. The voltageboost is due to the asymmetric nature of single-phase loads. Some of thevoltage boost is an increase in the fundamental frequency voltage, andsome is due to harmonic interactions. Ideally, the greatest increase infundamental voltage occurs when the peak of the harmonic voltages is inphase with the peak of the fundamental. This provides the greatestincrease in peak voltage from the exciter, which in turn will becaptured by the capacitor in the system, and maintain a CV output.

[0055] The model is based on the standard d-q machine model, with aresistive load, (1.0 pf) such as the auxiliary output winding would haveapplied to it. It is assumed that only fundamental frequency voltagesand currents flow in the auxiliary output winding. The single phase loadcurrent induces second harmonic currents in the field winding, thesecond harmonic currents in the field winding induce third harmonicvoltages in all the stator windings, not just the exciter winding. Thirdharmonic voltages in the output winding applied to a resistive load giverise to third harmonic load currents. Third harmonic load currentsinduce fourth harmonic currents in the field winding. Fourth harmonicfield currents induce fifth harmonic voltages in the stator winding,etc.

[0056] The ideal model is an infinite series of harmonics—even harmonicsin the field winding and odd harmonics in the stator winding. While theideal model could be used and might be appropriate in somecircumstances, for the preferred embodiment using only the dominantthird harmonic (and ignoring greater harmonics) does not introducesignificant error and is sufficient. The effects of current flowing inthe exciter windings are also ignored, as this current is not large andwill not have a great effect. One potential error is due to the effectsof magnetic saturation which may be different in the d and q axis. Themodel is applied to the loaded output winding first, and these resultsare used to complete the analysis for another stator winding.

[0057] Referring now to FIG. 7, a diagram used in developing ageneralized model is shown, and the following definition are usedtherein:

[0058] θ=angle of the d axis relative to phase A

[0059] θ=ωt−β

[0060] β=position of the rotor at t=0

[0061] δ=Torque angle

[0062] i_(a)=Phase A, (auxiliary output) current

[0063] V_(a)=Phase A, (auxiliary output) voltage

[0064] i_(d)=direct axis current

[0065] i_(q)=Quadrature axis current

[0066] i_(z)=zero sequence current

[0067] L_(fd)=Mutual inductance, field to I axis

[0068] L_(f)=Field self inductance, including leakage

[0069] R_(f)=Field resistance

[0070] V_(f)=Field Voltage

[0071] L_(d)=d axis self inductance

[0072] V_(q)=q axis voltage

[0073] V_(d)=d axis voltage.

[0074] V₀=zero sequence voltage.

[0075] ψ_(d)=d axis flux linkages.

[0076] ψ_(q)=q axis flux linkage

[0077] L_(q)=q axis inductance

[0078] i_(f)=Field current

[0079] {acute over (ω)}=Angular rotation speed

[0080] δ=Torque Angle

[0081] E=Voltage behind reactance.

[0082] The transformation/definitions are:

[0083] i_(a)=I*cos{acute over (ω)}t (Reference)

[0084] V_(a)=R_(L)I*cos{acute over (ω)}t, (R_(L)=load resistance)

[0085] i_(b)=i_(c)=0

[0086] V_(a)=R_(L)I*cos{acute over (ω)}t=V_(d)*Cos({acute over(ω)}t−β)+V_(q)Sin({acute over (ω)}t−β)+V_(z)

[0087] i_(d)=⅔*I*cos{acute over (ω)}t*Cos({acute over (ω)}t−β)

[0088] i_(d)=⅔*I*½*(cos(2{acute over (ω)}t−β)+Cos β)

[0089] i_(q)=⅔*I*cos{acute over (ω)}t*Sin({acute over (ω)}t−β)

[0090] i_(q)=⅔*I*½*(Sin(2{acute over (ω)}t−β)+Sin(−β))

[0091] i_(q)=⅔*I*½*(Sin(2{acute over (ω)}t−β)−Sin β)

[0092] i_(d)=I/3*Cos(2{acute over (ω)}t−β)+I/3*cos β

[0093] i_(q)=I/3*Sin(2{acute over (ω)}t−β)−I/3*Sin β

[0094] i_(z)=I/3*Cos{acute over (ω)}t

[0095] The field voltage equation is:

V _(f) =L _(fd) pi _(d) +R _(f) +pL _(f))*i _(f)

[0096] where p is the derivative operator. For dc p=0, which results in:

V _(f)(dc)=R _(f) I _(f)(dc)

[0097] The ac solution is more complicated:

pi _(d) =−I/3*sin(2{acute over (ω)}t−β)*(2{acute over (ω)})

0=L _(fd)*(−I/3)*(2{acute over (ω)})*sin(2{acute over (ω)}t−β)+j2{acuteover (ω)}i _(f) L _(f)

[0098] (R_(f) compared to j2{acute over (ω)}L_(f) may be ignored)

0=(−I/3)*L _(fd)*(−j)*(2{acute over (ω)}t)∠−β+j*(2{acute over (ω)}t)i_(f) L _(f)

0=(I/3)*L _(fd) ∠−β=I _(f) L _(f)

i _(f) =I/3*L _(fd) /L _(f) ∠−β=−I/3*L _(fd) /L _(f) cos(2{acute over(ω)}t−β)

i _(f) =I _(f) −I/3*L _(fd) /L _(f)*cos(2{acute over (ω)}t−β)

[0099] (Superposition of the Two Solutions)

[0100] Given i_(d), i_(f) and i_(q), flux linkages may be calculated.ψ_(d) is the direct axis flux:

ψ_(d) =L _(fd) *[I _(f) −I/3*L _(fd) /L _(f)*cos(2{acute over(ω)}t−β)]+L _(d) *[I/3*cos(2{acute over (ω)}t−β)+I/3*cos β]

[0101] ψ_(q) is the quadrature axis flux:

ψ_(q) =L _(q) *[I/3*sin(2{acute over (ω)}t−β)−I/3*sin β]

[0102] The axis voltage equations are:

V _(d) =pψ _(d)+{acute over (ω)}ψ_(q)

V _(q)=−{acute over (ω)}ψ_(d) +pψ_(q)

V ₀ =Lo*pi _(z)

[0103] Substituting provides:

V _(d)=(2{acute over (ω)})*L _(fd) ² /L _(f) *I/3*sin(2{acute over(ω)}t−β)−2{acute over (ω)}L _(d) *I/3*sin(2{acute over (ω)}t−β)+{acuteover (ω)}L _(q) *I/3*Sin(2{acute over (ω)}t−β) −{acute over (ω)}L _(q)*I/3*sin β

V _(q) =−{acute over (ω)}L _(fd) *[I _(f) −I/3*L _(fd) /L_(f)*cos(2{acute over (ω)}t−β)]−{acute over (ω)}L _(d) *[I/3*cosβ+I/3*cos(2{acute over (ω)}t−β)+(2{acute over (ω)}L _(q) *I/3*cos(2{acute over (ω)}t−β)

V ₀ =−{acute over (ω)}L _(o) *I/3*sin{acute over (ω)}t

V _(d) =[I/3*2{acute over (ω)}*L _(fd) ² /L _(f) −I/3*2{acute over(ω)}*L _(d) +I/3*{acute over (ω)}*L _(q)]*sin(2{acute over(ω)}t−β)−I/3*{acute over (ω)}L _(q)sin β

V _(d) =[I/3*2{acute over (ω)}*(L _(fd) ² /L _(f) −L _(d))+I/3{acuteover (ω)}*L _(q)]*sin(2{acute over (ω)}t−=)− I/3*{acute over (ω)}*L_(q)*sin β

V _(d) =I/3*X _(T)*Sin(2{acute over (ω)}t−β)−I/3*X _(q)*sin β,

[0104] Where

X _(T)=(L _(fd) ² /L _(f) −L _(d))*2{acute over (ω)}+{acute over (ω)}L_(q) and X _(q) ={acute over (ω)}L _(q).

V _(q) =−{acute over (ω)}L _(fd) I _(f) {acute over (ω)}L _(d) *I/3*cosβ+[{acute over (ω)}L _(fd) ² /L _(f) −{acute over (ω)}L _(d)+2{acuteover (ω)}L _(q) ]*I/3*cos(2{acute over (ω)}t−β)

V _(q) =−E−X _(d) *I/3*cos β+X _(N) *I/3*cos*(2{acute over (ω)}t−β)

[0105] Where

{acute over (ω)}L _(fd) I _(f) =E, {acute over (ω)}L _(d) =X _(d), and{acute over (ω)}L _(fd) ² /L _(f) −{acute over (ω)}L _(d)+2{acute over(ω)}L _(q) =X _(N)

[0106] In summary:

V _(d) =I/3*X _(T)*sin(2{acute over (ω)}t−β)−I/3*X _(q)*sin β

V _(q) =−E−X _(d) *I/3*cos β+X _(N) *I/3*cos*({acute over (ω)}t−β)

V ₀ =−X ₀ *I/3*sin {acute over (ω)}t

[0107] Inverse transforms may be used to find a phase voltage:

V _(a) =V _(d)*cos({acute over (ω)}t−β)+V _(q)*sin ({acute over(ω)}t−β)+V ₀

V _(a) =[I/3*X _(T)*sin*(2{acute over (ω)}t−β)−I/3*X _(q)*sinβ]*cos({acute over (ω)}t−β)+[−E−X _(d) *I/3*cos β+X _(N) *I/3*cos({acuteover (ω)}t−β)]*sin({acute over (ω)}t−β)−X ₀ *I/3*sin {acute over (ω)}t

V _(a) =I/3*X _(T)*sin(2{acute over (ω)}t−β)*cos({acute over(ω)}t−α)−I/3*X _(q)*sin*cos({acute over (ω)}t−β)+−E*sin({acute over(ω)}t−β)−X _(d) *I/3*cos β*sin({acute over (ω)}t−β)+X _(N)*I/3*cos(2{acute over (ω)}t−β)*sin({acute over (ω)}t−β)−X ₀ *I/3*sin{acute over (ω)}t

V _(a) =I/3*X _(T)*½*[sin(3{acute over (ω)}t−2β)+sin {acute over(ω)}t]−I/3*X _(q)*sin β*cos({acute over (ω)}t−β)−E*sin({acute over(ω)}t−β)−X _(d) *I/3*cos β*sin({acute over (ω)}t−β)+I/3*X_(N)*½*[sin(3{acute over (ω)}t−2β)+−sin {acute over (ω)}t]−X ₀ *I/3*sin{acute over (ω)}t

[0108] Collecting the fundamental terms yields:

V _(a) =−E*sin({acute over (ω)}t−β)−X _(d*) I/3*cos β*sin({acute over(ω)}t−β)−I/3*X _(q)*sin β*cos({acute over (ω)}t−β)+I/3*X _(T*)½*sin{acute over (ω)}t−I/3*X _(N*)½*sin {acute over (ω)}t−X _(0*) I/3*sin{acute over (ω)}t

[0109] Phasors, cosine references Sin {acute over (ω)}t=−j are:

jE∠−β+jX _(d) *I/3*cos β∠−β−I/3*X _(q)*sin β∠−β−jI/3*X _(T)*½*∠0+jI/3*X_(N)½*∠0+jX ₀ I/ ₃*∠0°

j=∠90

90−β=δ(δ=torque angle)

90−δ=β

V _(a) =E∠δ+X _(d) *I/3*cos β∠δ−I/3*X _(q)*sin β∠−β−I/3*X _(T)*½∠90+I/3*X _(N)*½*∠90 +I/3*X ₀*∠90°

I/3*cos β=I/3*cos(90−δ)=I/3*sin β=I _(d)

I/3*sin β=I/3*sin(90−δ)=I/3*cos β=I _(q)

V _(a) =E∠δ+X _(d) I _(d) ∠δ−X _(q) I _(q) ∠−β−I/3*X _(T)*½*∠90 +I/3*X_(N)*½*∠90 +I/3*X ₀∠90°.

[0110] The first three terms of V_(a) above are the voltage behindreactance, (E, and the X_(d)I_(d) are X_(q)I_(q) drops are from standardthree phase machine theory). The last three terms are due to theasymmetric nature of single phase loading. The sign of the current ischanged for a generator—(positive current flows out of the machine).

V _(a) =E∠δ−X _(d) I _(d) ∠δ+X _(q) I _(q) ∠−β+I/3*X _(T)*½*∠90−I/3*X_(N*)½*∠90−I/3*X ₀∠90

[0111] The last three terms may be treated similar to leakage reactancedrops:

I/3*½*∠90(X _(T) −X _(N))−I/3*X ₀∠90(X _(T) −X _(N) is <0 and|X_(N)|>|X_(T)|)

[0112] X_(T)−X_(N) can be shown to be approximately −{acute over(ω)}L_(q), as seen on the phasor diagram of FIG. 8.

[0113] The third harmonic voltages are calculated as follows:

I/3*X _(T)*½*sin(3{acute over (ω)}t−2β)+I/3*X _(N)*½*sin(3{acute over(ω)}t−2 β)

[0114] The sign is reversed for generator output current:

−I/3*½*(X _(T) +X _(N))sin(3{acute over (ω)}t−2β)

[0115] The phasing of the third harmonic relative to the fundamentaldepends on the torque angle δ. Voltage induced in another stator winding(i.e. exciter winding) at angle ζ relative to phase A is calculated asfollows:

Vs=V _(d)*cos ({acute over (ω)}t−β−ζ)+V _(q)*sin({acute over(ω)}t−β−ζ)+V ₀

Vs=[I/3*X _(T)*sin(2{acute over (ω)}t−β)−I/3*X _(q)sin β]*cos({acuteover (ω)}t−β−ζ)+[−E−X _(d) I/3*cos β+X _(N) I/3*cos(2{acute over(ω)}t−β)]*sin({acute over (ω)} t−β− Z)−X ₀ *I/3*sin({acute over (ω)}t)

Vs=I/3*X _(T)*sin(2{acute over (ω)}t−β)*cos({acute over (ω)}t−β−ζ)−I/3*X _(q)*sin β*cos({acute over (ω)}t−β−ζ)+−E*sin({acute over(ω)}t−β−ζ)−X _(d) *I/3*cos β*sin({acute over (ω)}t−β−ζ)+X _(N)*I/3*cos(2{acute over (ω)}t−β)*sin({acute over (ω)}t−β−ζ)+−x ₀*I/3*sin({acute over (ω)}t)

[0116] Collecting fundamental terms:

V _(s=) E*sin({acute over (ω)}t−β−ζ)−X _(d) I/3*cos β*sin({acute over(ω)}t−β−ζ)−I/3*X _(q)sin β*cos({acute over (ω)}t−β−ζ)−X ₀*I/3*sin({acute over (ω)}t)+I/3*X _(T)½*sin({acute over (ω)}t+ζ)−X _(N)*I/3*½*sin({acute over (ω)}t+ζ)

[0117] Phasor and cosine references are:

V _(s) =jE _(s)∠(−β−ζ)+jX _(d*) I/3*cos β∠(−β−ζ)−I/ _(3*) X _(q)*sinβ∠(−β−ζ)+jX ₀ *I/3*∠0−j*I/3*½*X _(T) ∠ζ+jX _(N*) I/3*½*∠ζ

V _(s) =E∠(90−β−ζ)+X _(d) *I/3*cos β∠(90−β−ζ)−I/3X _(q)*sin β∠(−β−ζ)+jX₀ *I/3*∠0 −j*I/3*½*X _(T) ∠ζ+jX _(N*) I/3*½*∠ζ

[0118] Reversing the sign for generator convention:

V _(s) =E _(s)∠(δ−ζ)−X _(d*) I _(d)*∠(δ−ζ)+I _(q) X _(q)/(−β−ζ)−jX ₀*I/3*∠0+I/3*½*(X _(T) −X _(N))∠(ζ+90)

[0119]FIG. 9 is a phasor diagram for fundamental components. The firstthree terms above are the fundamental voltage from phase A shifted backby angle ζ. The term I/3*½*(X _(T) −X _(N))∠ζ changes the final phase ofVs. X_(T)−X_(N) is negative (|X_(N)|>|X_(T)|). X_(T)−X_(N)∠0 shifts thephase by 180°. At the correct angle ζ, I/3*½*(X_(T)−X_(N)) can be inphase with V_(s) caused by E_(s)∠(δ−ζ)−X _(d) I_(d)∠(δ−ζ)+X_(q)I_(q)∠−(β−ζ) and thus add directly to its magnitude.This condition causes the fundamental voltage to be boosted. The correctangle ζ is given by:

180+90+Z=−Z

270=−2Z

−90=−2Z

Z=45°

[0120] Thus, according to the calculations, a winding 45° lagging tophase A would have the highest fundamental voltage. This agrees with theplacement of 40° lagging (determined empirically) for the auxiliaryexciter.

[0121] The third harmonic voltages are:

I/ 3*½*( X _(T) +X _(N))*sin 3 ({acute over (ω)}t−2β−ζ)

[0122] Reverse the sign of the current for generator convention:

−I/3*½*(X _(T) +X _(N))*sin(3{acute over (ω)}t−2β−ζ)

[0123] It is necessary to know the torque angle (δ) at the load point todetermine the exact phasing of the third harmonic relative to thefundamental. This can be calculated from the phaser diagram, with X_(d)and X_(q) determined at the load saturation point. For the preferredembodiment:

δ=35°

β=90−35=55

2β=110°

[0124] The third harmonic is then:

−I/3*½*(X _(T) +X _(N))*sin(3{acute over (ω)}t−110−ζ)

[0125] ζ=40° (from the previous analysis) results in the third harmonicbeing:

−I/3*½*(X _(T) +X _(N)) Sin(3{acute over (ω)}t−110−40)

[0126] The third harmonic reaches its positive peak when the argument ofthe sin function is −90°. Thus:

3{acute over (ω)}t−110−40=−90

3{acute over (ω)}t=60

{acute over (ω)}t=20°

[0127] Given {acute over (ω)}t=200, cos({acute over(ω)}t−40)=Cos(−20)=Cos(20)=0.94×peak value. Hence the peak of the thirdharmonic coincides closely with the peak of the fundamental voltage aswas empirically determined for the exciter winding lagging 40° to theauxiliary output winding placement.

[0128] Alternative embodiments include using empirically locating thedesired slots, calculating the location of the desired slots, or acombination thereof.

[0129] Numerous modifications may be made to the present invention whichstill fall within the intended scope hereof. Thus, it should be apparentthat there has been provided in accordance with the present invention amethod and apparatus for welding that fully satisfies the objectives andadvantages set forth above. Although the invention has been described inconjunction with specific embodiments thereof, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, it is intended to embrace all suchalternatives, modifications and variations that fall within the spiritand broad scope of the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
 1. An engine-driven welding power supply system comprising: a welding output winding; a welding exciter winding in magnetic communication with the welding output winding; an auxiliary output winding; an auxiliary exciter winding in magnetic communication with the auxiliary output winding; and a welding power supply in electrical communication with the welding output winding and the auxiliary output winding, wherein the welding power supply has a welding output and an auxiliary output.
 2. The engine-driven welding power supply system of claim 1 wherein the welding output winding and the auxiliary output winding are in magnetic communication.
 3. The engine-driven welding power supply system of claim 2, wherein the welding output windings and the auxiliary output windings are wound about a common stator.
 4. The engine-driven welding power supply system of claim 3, wherein the welding exciter winding and the auxiliary exciter winding are wound about the common stator.
 5. The engine-driven welding power supply system of claim 4, wherein the placement of the welding output winding, the auxiliary output winding, the welding exciter winding and the auxiliary exciter winding is such that the welding output and the auxiliary output are optimized.
 6. The engine-driven welding power supply system of claim 4, further comprising a field winding disposed to receive field current from the welding exciter winding and from the auxiliary exciter winding.
 7. The engine-driven welding power supply system of claim 6, further comprising a rectifier disposed between the welding exciter winding and the field winding, and further including a rectifier disposed between the auxiliary exciter winding and the field winding.
 8. The engine-driven welding power supply system of claim 2, further comprising a controller, connected to the welding power supply and the field winding.
 9. The engine-driven welding power supply system of claim 1, wherein the welding power supply includes a tapped reactor in electrical communication with the welding output winding and the welding output.
 10. The engine-driven welding power supply system of claim 1, wherein the welding output winding, the auxiliary output winding, the welding exciter winding and the auxiliary exciter winding are part of an AC generator.
 11. An engine-driven welding power supply system comprising: a welding output winding; means for providing a welding excitation current, in magnetic communication with the welding output winding; an auxiliary output winding; means for providing an auxiliary excitation current, in magnetic communication with the auxiliary output winding; and welding power supply means for receiving power from the welding output winding and the auxiliary output winding, and for providing a welding output and an auxiliary output.
 12. The engine-driven welding power supply system of claim 11 including a generator means for generating power, wherein the generator means includes the welding output winding, the auxiliary output-winding, the means for providing welding excitation current and the means for providing auxiliary excitation current.
 13. The engine-driven welding power supply system of claim 12, wherein the placement of the welding output winding, the auxiliary output winding, the welding exciter winding and the auxiliary exciter winding is such that the welding output and the auxiliary output are optimized.
 14. The engine-driven welding power supply system of claim 11, further comprising field means for providing a magnetic field in the generator, disposed to receive the welding and auxiliary excitation currents.
 15. The engine-driven welding power supply system of claim 14, further comprising a rectifier means for rectifying welding excitation current and the auxiliary excitation means.
 16. The engine-driven welding power supply system of claim 11, further comprising control means for controlling the welding power supply and the field current.
 17. A method of providing welding and auxiliary power comprising: turning a primary mover; inducing current in a welding output winding; inducing current in a welding exciter winding in magnetic communication with the welding output winding; inducing current in an auxiliary output winding; inducing current in an auxiliary exciter winding in magnetic communication with the auxiliary output winding; receiving the output of the welding output winding and providing a welding power output; and receiving the output of the auxiliary output winding and providing an auxiliary output.
 18. The method of claim 17 wherein inducing a current in the welding output winding also induces a current in the auxiliary output winding.
 19. The method of claim 18, wherein the welding output windings and the auxiliary output windings are wound about a common stator associated with a rotor, and wherein turning the primary mover turn the rotor.
 20. The-method of claim 19, wherein inducing a current in the welding exciter winding induces a current in the auxiliary exciter winding.
 21. The method of claim 20, further comprising determining where to place of the welding output winding, the auxiliary output winding, the welding exciter winding and the auxiliary exciter winding by determining what placement optimizes the welding output and the auxiliary output.
 22. The method of claim 20, further comprising providing a field current from the welding exciter winding and from the auxiliary exciter winding to a field winding.
 23. The method of claim 21, further comprising: rectifying an output of the welding exciter winding and providing it to a field winding; and rectifying an output of the auxiliary welding exciter winding and providing it to the field winding.
 24. The method of claim 18, further comprising controlling the welding power output by controlling a field winding current.
 25. The method of claim 18, further comprising selecting one of a plurality of range of welding power outputs by selecting a tap on a tapped reactor in electrical communication with the welding output winding and the welding output.
 26. The method of claim 17, further comprising generating AC power.
 27. An engine-driven power supply system comprising: an output winding; a first exciter winding in magnetic communication with the welding output winding; a second exciter winding in magnetic communication with the output winding; and a power supply in electrical communication with the output winding.
 28. The engine-driven power supply system of claim 27 further comprising a second output winding.
 29. An engine-driven welding power supply system comprising: a generator, including a stator with a plurality of slots; a welding output winding wound in a first subset of the plurality of slots, wherein a welding output winding magnetic axis is in a first direction; a welding exciter wound in a second subset of the plurality of slots, wherein a welding exciter .o winding magnetic axis is in a second direction; an auxiliary output winding wound in a third subset of the plurality of slots, wherein an auxiliary output winding magnetic axis is in a third direction; an auxiliary exciter winding wound in a fourth subset of the plurality of slots, wherein an auxiliary exciter winding magnetic axis is in a fourth direction; and a welding power supply in electrical communication with the welding output winding and the auxiliary output winding, wherein the welding power supply has a welding output and an auxiliary output.
 30. The engine-driven welding power supply system of claim 29, wherein the angle between the first direction and the second direction is such that a desired welding output is produced.
 31. The engine-driven welding power supply system of claim 30, wherein the angle between the third direction and the fourth direction is such that a desired auxiliary output is produced.
 32. The engine-driven welding power supply system of claim 29, wherein the angle between the first direction and the second direction is such that a welding exciter winding voltage increases as the welding output winding is loaded.
 33. The engine-driven welding power supply system of claim 32, wherein the angle between the third direction and the fourth direction is such that an auxiliary exciter winding voltage increases as the auxiliary output winding is loaded.
 34. The engine-driven welding power supply system of claim 33, wherein the angle between the third direction and the fourth direction is empirically determined.
 35. The engine-driven welding power supply system of claim 33, wherein the angle between the third direction and the fourth direction is calculated.
 36. An method of designing an engine-driven welding power supply system having a generator with a stator with a plurality of slots, a welding output winding, a welding exciter wound, an auxiliary output winding, and an auxiliary exciter winding, comprising: winding the welding output windings in a first subset of the plurality of slots such that the welding output winding has a first magnetic axis is in a first direction; winding the welding exciter windings in a second subset of the plurality of slots such that the welding exciter winding has a second magnetic axis is in a second direction; winding the auxiliary output windings in a third subset of the plurality of slots such that the auxiliary output winding has a third magnetic axis is in a third direction; winding the auxiliary exciter windings in a fourth subset of the plurality of slots such that the auxiliary exciter winding has a fourth magnetic axis in a fourth direction; and attaching a welding power supply in electrical communication with the welding output winding and the auxiliary output winding, wherein the welding power supply has a welding output and an auxiliary output.
 37. The method of claim 36, wherein the angle between the third direction and the fourth direction is empirically determined to provide a desired auxiliary output.
 38. The method of claim 36, wherein the angle between the third direction and the fourth direction is calculated to increase an auxiliary exciter winding voltage as the auxiliary output winding is loaded.
 39. An engine-driven power supply system comprising: a plurality of output windings in a first plurality of slots; a plurality of exciter windings in magnetic communication with the plurality of output windings in a second plurality of slots, wherein the location of the first and second plurality of slots is such that a desired output is produced; and a power supply in electrical communication with the output windings.
 40. The engine-drive power supply system of claim 39, wherein there are as many or more windings in the plurality of exciter windings as there are windings in the plurality of output windings. Yb
 41. An engine-driven welding power supply comprising: means for turning a primary mover; means for inducing current in a welding output winding, mechanically connected to the means for turning connected; means for inducing current in a welding exciter winding in magnetic communication with the welding output winding; means for inducing current in an auxiliary output winding; means for inducing current in an auxiliary exciter winding in magnetic communication with the auxiliary output winding; means for receiving the output of the welding output winding and providing a welding power-,output, electrically connected to the welding output winding; and means for receiving the output of the auxiliary output winding and providing an auxiliary output. 